CamGFR v2: a new model for estimating the glomerular filtration rate from standardized or non-standardized creatinine in patients with cancer

Abstract

Purpose: Management of patients with cancer, specifically carboplatin dosing, requires accurate knowledge of glomerular filtration rate (GFR). Direct measurement of GFR is resource-limited. Available models for estimated GFR (eGFR) are optimized for patients without cancer and either isotope dilution mass spectrometry (IDMS)- or non-IDMS-standardized creatinine measurements. We present an eGFR model for patients with cancer compatible with both creatinine measurement methods. Methods: GFR measurements, biometrics, and IDMS- or non-IDMS-standardized creatinine values were collected for adult patients from three cancer centers. Using statistical modelling, an IDMS- and non-IDMS creatinine compatible eGFR model (CamGFR v2) was developed. Its performance was compared to that of the existing models CKD-EPI, MDRD, FAS, Lund-Malmo Revised and CamGFR v1 using statistics for bias, precision, accuracy, and clinical robustness. Results: 3,083 IDMS- and 4,612 non-IDMS-standardized creatinine measurements were obtained from 7,240 patients. IDMS-standardized creatinine values were lower than non-IDMS-standardized values in within-centercomparisons (13.8% lower in Cambridge, p<0.0001; 19.3% lower in Manchester, p <0.0001), and more consistent between centers. CamGFR v2 was the most accurate (root-mean-squared error for IDMS = 14.97ml/min[95% CI 13.84,16.13]; non-IDMS = 15.74ml/min[14.86,16.63]), most clinically robust (proportion with >20% error of calculated carboplatin dose for IDMS = 0.12[0.09, 0.14]; non-IDMS = 0.17[0.15, 0.2]) and least biased (median residual for IDMS = 0.73ml/min[-0.68,2.2]; non-IDMS = -0.43ml/min[-1.48,0.91]) eGFR model, particularly when eGFR was larger than 60ml/min. Conclusions: CamGFR v2 can utilize IDMS- and non-IDMS-standardized creatinine measurements and outperforms previous models. CamGFR v2 should be examined prospectively as a practice-changing standard of care for eGFR-based carboplatin dosing.